On the SNES game jam they have a single download with all entries in it, is there s similar link for the Game Boy Jam?

The entries are all collected in the gbcompo21 github repo: https://github.com/gbdev/gbcompo21/tree/main/entries

You can either git clone that, or have github create a zip file of the repo (from the root repo page). https://github.com/gbdev/gbcompo21/archive/refs/heads/main.zip